Fowl play: California’s drought fingered in bird deaths

Native pigeons and waterfowl fall victim to avian disease.

The casualty was a band-tailed pigeon, Patagioenas fasciata: pale gray shoulders, black primary feathers, a glint of iridescent green at the neck. The bird, a member of California’s only native pigeon species, lay prone beneath a live oak on Kawahara’s family’s farm west of San Jose. Kawahara, a shaggy-haired wildland firefighter, took a few pictures and uploaded them to Facebook. Some ecologists he knew suggested he preserve the animal for science, so Kawahara stuffed it in a Tupperware, slid it into his freezer, and went hiking. By the time he got back, his father and grandmother had collected four more pigeons for examination.

Band-tailed pigeon populations have been declining in California for decades, and scientists think disease is among the culprits. Photo by Monte Kawahara.

A few days later, Kawahara came across a live band-tailed pigeon in the throes of illness. The creature hopped feebly away at his approach, but couldn’t fly; soon it, too, was dead. Kawahara packed five pigeons in a cooler and drove them to a Berkeley museum, which wanted the birds for its collection, though it couldn’t ascertain cause of death. “I felt helpless,” Kawahara said. He’d been raised on this farm and considered himself one of its stewards; the strange fatalities troubled him. “There I was, birds were dying, and I couldn’t solve this mystery.”

A hundred miles north, however, Krysta Rogers had already cracked the case. Two weeks before Christmas, Rogers, an environmental scientist at the California Department of Fish and Wildlife in Rancho Cordova, began receiving dead pigeons from biologists, wildlife rehab centers and landowners around the state. When Rogers necropsied the specimens, she found their upper digestivetracts packed with crumbly lesions the consistency of cheese. DNA analysis confirmed her hunch: The birds were dying from avian trichomonosis, a disease caused by a protozoan parasite that followed city pigeons to the United States from Europe long ago. Stricken birds starve, suffocate, or grow too weak to escape predators.

Rogers had seen trichomonosis outbreaks before, but this winter’s was exceptional. By early March, she’d received reports from San Diego County to Mendocino County — 22 counties altogether, the most ever. She estimated that 10,000 band-tailed pigeons had perished. The massive die-off, Rogers suspected, had been abetted by California’s debilitating drought. As water sources go dry, birds congregate around remaining oases, like fountains and irrigation ditches. In such close quarters, disease spreads quickly. “It’s the same reason you end up with a cold after sitting next to a coughing person on an airplane,” Rogers said.

The die-off was a troubling development for band-tailed pigeons, a bird whose population has been dwindling for decades due partly to habitat loss and naturally slow reproduction. Trichomonosis is especially damaging because it strikes in winter, when the birds are gathered in flocks but before they’ve had a chance to mate. The disease has a grim track record: Some scientists suspect that it helped finish off the band-tailed’s close relative, the passenger pigeon.

Rogers and her colleagues urged landowners to take down birdbaths and feeders to slow the parasite’s advance. But the drought was a formidable foe: 2014 was the hottest, driest year in California’s recorded history. According to Rogers, outbreaks occur more frequently in such years; given the Golden State’s climatological trends, therefore, it’s little wonder that trichomonosis rates appear to be rising. From 1950 to 2005, the state suffered mortality episodes in just 12 individual years. The 10 years since, however, have seen seven outbreaks.

What’s more, trichomonosis is far from the only avian disease exacerbated by drought. At the Tule Lake National Wildlife Refuge, just south of the Oregon border, U.S. Fish and Wildlife Service biologist John Beckstrand spent last summer and fall scooping up infectious, maggot-ridden waterfowl carcasses, trying to control an outbreak of avian botulism. Although botulism erupts at Tule Lake two of every three years, last fall’s die-off was unusually severe — likely because the wetlands of nearby Lower Klamath National Wildlife Refuge had dried up for the second year in a row, their precious water diverted to farmers with senior rights. Migrating ducks and geese flocked to Tule Lake instead, where hot temperatures had created favorable conditions for botulism spores. Ultimately, some 20,000 birds may have succumbed at the refuge.

Waterfowl take flight at the Tule Lake National Wildlife Refuge, where an estimated 20,000 birds died in an avian botulism outbreak last summer and fall. Photo courtesy of the U.S. Fish and Wildlife Service.

As if that weren’t enough, the refuge’s geese and swans have also been plagued by avian cholera. Though cholera used to explode in autumn, the area is dry enough that many migrating birds bypass it altogether in fall. These days, waterfowl densities — and cholera rates — are highest in spring. “Now you start seeing it in February, and you could be dealing with it for two and a half months,” Beckstrand said. Other sites are coping with similar problems: In February, cholera turned up at Nevada’s Walker Lake for the first time in decades, and in mid-March the disease claimed 2,000 snow geese in Idaho.

Meanwhile, now that it’s spring, trichomonosis appears to have nearly run its course — for this year, anyway. Though scientists worried the disease might spill over into raptors, that fear didn’t come to pass. By late February, band-tailed pigeons had already begun decamping Kawahara’s farm for their northern breeding grounds, and the hills had fallen silent.

Some birds, though, wouldn’t make the trip. In a dappled grove of coast live oak and redwoods, a month after the outbreak began, Kawahara gestured to a matted, feathery carcass melting into the soil. “Everything’s wrapped up in this: Drought, development, introduced species,” he said as he ran a stick along the pigeon’s exposed spine. “What does this say about the health of the land?”